Spinning underwater vortices, known as submesoscale storms, are responsible for 20 percent of the ice melt under the Thwaites glacier's ice shelf in Antarctica. These features trap warm deep water beneath the ice, accelerating melting in a feedback loop. As the climate warms, they could intensify and contribute to greater sea level rise than previously anticipated.
The Thwaites glacier, often called the 'doomsday' glacier due to its potential to raise global sea levels by 65 centimetres if it collapses, loses 50 billion tonnes of ice annually. Researchers have identified underwater 'storms'—vortices up to 10 kilometres wide—as key drivers of this melt. These submesoscale features form when ocean waters of differing densities or temperatures collide, similar to how hurricanes develop in the atmosphere.
Mattia Poinelli at the University of California, Irvine, explains: “They have so much motion, and they’re really hard to stop. So the only way they could go is just get trapped under the ice.” Once trapped in the cavity beneath the ice shelf, the vortices push colder surface water outward, drawing up warmer, saltier deep water that melts the ice from below. This process releases fresh meltwater, which interacts with the warm water to intensify the vortex's spin, creating a feedback loop that boosts further melting.
Modelling by Poinelli and colleagues revealed that these storms accounted for one-fifth of the total melt across the Thwaites and neighbouring Pine Island ice shelves over nine months. This marks the first quantification of their impact on an entire ice shelf. Ice shelves like Thwaites act as brakes on glacier flow into the sea and shield them from waves.
Supporting evidence comes from a 2022 incident where a deep-water float was captured by an eddy under the Stancomb-Wills ice tongue. Cathrine Hancock at Florida State University and her team estimated such eddies cause 0.11 metres of annual melt there. Hancock notes: “It shows that the concept of an eddy spinning down underneath an ice shelf is important.” She suggests similar effects from smaller storms require better quantification.
As global warming increases fresh meltwater around Antarctica, these underwater storms are expected to strengthen. Tiago Dotto at the UK National Oceanography Centre describes the findings as “astonishing” and urges more under-ice observations, especially amid changing wind patterns and sea ice. The study appears in Nature Geoscience (DOI: 10.1038/s41561-025-01831-z).